the joy of discovery, enhanced by my growing appreciation of the city’s unique assortment of street trees. Each block had the potential for something new, and just as some people delight in coming upon a stunning Victorian home, a thriving Ginkgo biloba did the same for me.
I hope this book brings the same joy to those of you who live here and to those who are visiting. For San Franciscans, this book offers an easy opportunity to learn about the trees you pass by every day, trees that form the living part of our outdoor architecture. For the tourist (especially if you’re from the land of maples and beeches, like me), this book can open a door to the new and the exotic.
TREES can have a hard time in San Francisco. Before the arrival of the Spanish to the Bay Area in the late 18th century, San Francisco was largely treeless. Only a few live oaks and willows huddled in wind-sheltered valleys interrupted the expanse between the San Francisco Bay and the Pacific Ocean. In fact, according to historian Hubert Bancroft, the Spanish explorers described the area as “the very worst place [for settlement] in all California … since the peninsula afforded neither lands, timber, wood, nor water, nothing but sand and brambles and raging winds.” To understand what the city looked like in its natural state 200 years ago, just gaze across the Golden Gate to the Marin Headlands, where you’ll see grassy, windswept hills—and no trees.
San Francisco’s urban forest is a relatively recent phenomenon. Early tree-planting efforts focused almost exclusively on public parks. Beginning in 1870, the creation of Golden Gate Park out of acres of sand dunes was the most ambitious of these efforts. Landscape architect Frederick Law Olmsted, designer of New York’s Central Park, submitted an early plan for a great city park in 1865. His design was rejected, and Olmsted later warned: “There is not a full grown tree of beautiful proportions near San Francisco, nor have I seen any young trees that promised fairly, except, perhaps, certain compact clumpy forms of evergreens, wholly wanting in grace and cheerfulness. It would not be wise nor safe to undertake to form a park upon any plea which assumed as a certainty that trees which would delight the eye can be made to grow near San Francisco.” In spite of Olmsted’s warnings, the city persevered. The design job went to 24-year-old William Hammond Hall (later the park’s first superintendent), and Golden Gate Park became the celebrated heart of San Francisco’s urban forest.
Despite early successes creating tree-filled parks, San Franciscans left their streets bare for many more years. Look at any photograph of the city’s neighborhoods as recently as the 1960s, and the lack of trees will be striking. Things began to change in the late 1960s and 1970s when San Francisco (a center of the growing environmental movement) began city-sponsored street tree plantings in the neighborhoods. City arborists involved with the new program had to learn, through trial and (frequently) error, which trees would thrive in San Francisco’s unique climate and topography. Early tree-planting efforts focused on a very few trees (ficus, blackwood acacia, Myoporum, and others) selected for their rapid growth rates and tolerance of coastal conditions. Unfortunately, many of these fast-growing trees quickly developed into “green monsters” that buckled sidewalks, crowded narrow street setbacks, and (unforgivable in San Francisco) blocked views.
In 1981, things took a turn for the worse, as a municipal budget cut eliminated tree- planting programs in most of the neighborhoods. Tree-hugging residents responded by forming Friends of the Urban Forest, a volunteer-based nonprofit organization, to step into the breach and continue the greening of San Francisco. One of the country’s oldest urban forestry organizations, this group conducts weekly Saturday-morning programs where volunteers and residents collaborate to plant and care for street trees. In addition to the energy and enthusiasm of its volunteers, Friends of the Urban Forest offers growing expertise in recommending tree species appropriate for the city.
That expertise is important because of the unique geographic and climatic conditions that make San Francisco a challenging environment for trees. The city’s climate is typically Mediterranean, with cool, wet winters and a long, cool dry season; the average high temperature in July is only 14°F higher than in January. Our location at the Golden Gate, a gap in California’s coastal range, adds even more unusual weather patterns. The summertime contrast between the cool, moist offshore air rushing through that gap and the warmer air rising from California’s inland valleys creates the city’s famous fog, as well as the sustained winds that make San Francisco the real Windy City (sorry, Chicago). If this weren’t enough, the topography here creates further challenges. The western neighborhoods closest to the ocean have the most wind and fog and, being built on former sand dunes, the sandiest (nutrient-poor) soils. The eastern, bay-facing neighborhoods are much sunnier, have better soils, and are less windy because they are sheltered by the hills to the west.
Also contributing to the challenges for trees is the fact that San Francisco is the most densely populated U.S. city west of Manhattan, with little room for grassy medians or lawns. As a result, street trees are almost always planted in small cuts in the sidewalks, in compacted soil that many species cannot tolerate. In addition, narrow streets and overhead wires often leave no room for large tree canopies. Finally, San Franciscans love their views, so when it comes to a choice between tall trees and vistas to the ocean or bay, trees often lose out.
So San Francisco’s trees have to be able to handle:
sandy soils set in cement,
driving wind,
foggy summers,
seven months a year without rain,
and attacks from view-conscious residents.
It’s hardly a place for maples and beeches. But through decades of trial and error, San Franciscans have discovered and welcomed a unique mix of trees from around the world that thrive in our unusual conditions. This book introduces those trees to you.
Liquidambar styraciflua
AMERICAN SWEETGUM
If, like me, you’re from east of the Mississippi and associate trees with leafy maples, this is your Bay Area substitute. Although native to the humid Southeastern United States, Mexico, and Central America, American sweetgum thrives in San Francisco’s Mediterranean climate. Its medium green, distinctive maplelike leaves turn yellow, orange, and red in the fall, although the colors are not as brilliant in San Francisco as in warmer inland climates. It is considered a deciduous tree, but some sweetgums retain their old leaves until the following spring, when new leaves arrive, while other specimens are leafless all winter—it just depends on the tree. The reason has to do with the broad native range of the tree; that is, specimens with forebears from the southern part of the tree’s range are more likely to retain their leaves year-round than those with northern ancestors, which adapted to colder winters. American sweetgums have insignificant flowers, followed by round, spiny seed capsules in the winter. This is one of San Francisco’s larger street trees, growing in an oval form to 40–50 feet in height. Pest and disease resistant, this is a great choice for a street tree if you don’t mind some sidewalk damage from its invasive roots. With long, straight trunks, sweetgums are an important timber tree in the Southeast; the wood is used for furniture, cabinets, and veneers.
LOCATION: 2503–2507 Bryant St./23rd St. in the Mission; also many examples on Stanyan St. between 17th and Belgrave Sts. in Cole Valley
The Down Under Connection
